Flexible DMRG-based framework for anharmonic vibrational calculations

TL;DR

This paper introduces a flexible vDMRG framework for anharmonic vibrational calculations, capable of handling complex potential energy surfaces and excited states, demonstrated on a challenging molecule with 24 vibrational modes.

Contribution

The authors develop an extended n-mode vDMRG method supporting general PES forms, optimized vibrational basis sets, and excited-state calculations, advancing anharmonic vibrational analysis.

Findings

Successfully applied to methyloxirane with 24 vibrational modes

Achieved accurate anharmonic transition frequencies

Demonstrated flexibility in basis set and PES representations

Abstract

We present a novel formulation of the vibrational density matrix renormalization group (vDMRG) algorithm tailored to strongly anharmonic molecules described by general high-dimensional model representations of potential energy surfaces. For this purpose, we extend the vDMRG framework to support vibrational Hamiltonians expressed in the so-called $n$-mode second-quantization formalism. The resulting $n$-mode vDMRG method offers full flexibility with respect to both the functional form of the PES and the choice of the single-particle basis set. We leverage this framework to apply, for the first time, vDMRG based on an anharmonic modal basis set optimized with the vibrational self-consistent field algorithm on an on-the-fly constructed PES. We also extend the $n$-mode vDMRG framework to include excited-state targeting algorithms in order to efficiently calculate anharmonic transition frequencies. We demonstrate the capabilities of our novel $n$-mode vDMRG framework for methyloxirane, a challenging molecule with 24 coupled vibrational modes.